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Abstract:

A surgical fixation system having an improved mechanism to prevent the
back out of screws employed in securing a surgical fixation plate to an
intended orthopedic location.

Claims:

1. A surgical fixation system for fixing a first bony segment relative to
a second bony segment, comprising: a bone plate sized to span at least
two adjacent bony segments, said bone plate including a first aperture
configured to receive an anchor element, said first aperture positioned
relative to said first bony segment, and a second aperture configured to
receive an anchor element, said second aperture positioned relative to
said second bony segment; a plurality of anchor elements configured to
anchor said bone plate to said first and second bony segments, each of
said anchor elements dimensioned to be received through one of said first
and second apertures; and a plurality of unbroken annular anti-backout
elements disposed within each of said first and second apertures, said
anti-backout elements configured to allow passage of at least a portion
of said anchor element therethrough in one direction while resisting
passage of at least a portion of said anchor element therethrough in an
opposite direction.

3. The surgical fixation system of claim 1, wherein said anchor element
comprises a bone screw having a head region and threaded shaft region.

4. (canceled)

5. The surgical fixation system of claim 3, wherein said head region
further includes a circumferential recess.

6. The surgical fixation system of claim 5, wherein said bone screw
further comprises a washer member disposed within said circumferential
recess.

7. The surgical fixation system of claim 6, wherein said washer member
comprises an unbroken ring having a generally planar upper surface having
a first circumference, a lower surface having a second circumference less
than said first circumference, and a generally angled lateral surface
extending between said upper and lower surfaces.

8. The surgical fixation system of claim 7, wherein said upper surface is
configured to interact with said anti-backout element.

9. The surgical fixation system of claim 6, wherein said recess has a
height dimension greater than a height dimension of said washer member.

10. The surgical fixation system of claim 1, further comprising third and
fourth apertures configured to receive an anchor element, said third
aperture positioned adjacent said first aperture and relative to said
first bony segment, said fourth aperture positioned adjacent said second
aperture and relative to said second bony segment.

11. The surgical fixation system of claim 1, further comprising a lip
member positioned on a bone engaging surface of said plate, said lip
member configured to engage a portion of said first bony segment.

12. The surgical fixation system of claim 1, further comprising a
plurality of anti-migration features positioned on a bone engaging
surface of said plate, said anti-migration features comprising a series
of ridges positioned around said first and second apertures.

13. The surgical fixation system of claim 12, wherein said anti-migration
features are positioned around said first aperture in a radial pattern.

14. The surgical fixation system of claim 13, wherein said anti-migration
features are positioned around said second aperture in an alignment
generally parallel to a central longitudinal axis of said bone plate.

15. A method of performing spinal fusion surgery, comprising: providing a
bone plate sized to span at least one intervertebral disc space between
adjacent first and second vertebral bodies, said bone plate having a
first end including a first aperture configured to receive an anchor
element, a second end including a second aperture configured to receive
an anchor element, a first canted coil ring disposed within said first
aperture, and a second canted coil ring disposed within said second
aperture, said first and second canted coil rings configured to allow
passage of at least a portion of said anchor element therethrough in one
direction while resisting passage of at least a portion of said anchor
element therethrough in an opposite direction; positioning said bone
plate against a spinal column such that said first end is adjacent said
first vertebral body and said second end is adjacent said second
vertebral body; advancing a first anchor element through said first coil
ring within said first aperture such that said first canted coil ring
covers at least a portion of said first anchor element; and advancing a
second anchor element through said second canted coil ring within said
second aperture such that said second canted coil ring covers at least a
portion of said second anchor element.

16. (canceled)

17. The method of claim 15, wherein said first and second anchor elements
each comprise bone screw having a head and a threaded shaft.

18. (canceled)

19. The method of claim 17, wherein said head further includes a
circumferential recess.

20. The method of claim 19, wherein said bone screw further comprises a
washer member disposed within said circumferential recess.

21. The of claim 20, wherein said washer member comprises an unbroken
ring having a generally planar upper surface having a first
circumference, a lower surface having a second circumference less than
said first circumference, and a generally angled lateral surface
extending between said upper and lower surfaces.

22. The method of claim 21, wherein said upper surface is configured to
interact with said canted coil ring after advancement of said bone screw
through one of first and second apertures.

23. The method of claim 20, wherein said recess has a height dimension
greater than a height dimension of said washer member.

24. The method of claim 15, further comprising third and fourth apertures
configured to receive an anchor element, said third aperture positioned
adjacent said first aperture and relative to said first bony segment,
said fourth aperture positioned adjacent said second aperture and
relative to said second bony segment.

25. The method of claim 15, further comprising a lip member positioned on
a bone engaging surface of said plate, said lip member configured to
engage a portion of said first bony segment.

26. The method of claim 15, further comprising a plurality of
anti-migration features positioned on a bone engaging surface of said
plate, said anti-migration features comprising a series of ridges
positioned around said first and second apertures.

27. The method of claim 26, wherein said anti-migration features are
positioned around said first aperture in a radial pattern.

28. The method of claim 27, wherein said anti-migration features are
positioned around said second aperture in an alignment generally parallel
to a central longitudinal axis of said bone plate.

29. The method of claim 21, wherein said lower surface is configured to
interact with said canted coil ring upon advancement of said bone screw
though one of said first and second apertures to increase an inner
circumference of the canted coil ring and facilitate passage of the bone
screw therethrough.

Description:

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] The present application is an international patent application
claiming the benefit of priority from U.S. Provisional Application Ser.
No. 60/965,589, filed on Aug. 20, 2007 and U.S. Provisional Application
Ser. No. 61/057,793, filed on May 30, 2008, the entire contents of which
are hereby expressly incorporated by reference into this disclosure as if
set forth fully herein.

BACKGROUND OF THE INVENTION

[0002] I. Field of the Invention

[0003] The present invention relates generally to the area of surgical
fixation, and more particularly to a surgical fixation system having an
improved mechanism to prevent the back out of screws employed in securing
a surgical fixation plate to an intended orthopedic location.

[0004] II. Discussion of the Prior Art

[0005] The use of surgical fixation systems involving plates is accepted
practice for a variety of orthopedic procedures. One procedure
experiencing proliferated growth is that of spinal fusion, wherein a
surgical fixation plate is secured along two or more vertebral bodies
through the use of screws or fasteners extending through bores formed in
the plate. Secured in this fashion, the surgical fixation plates serve to
immobilize the vertebral bodies. When employed with bone allograft or
another fusion-effecting implant (such as a mesh cage, a threaded cage,
etc. . . . ), this immobilization promotes fusion to occur between the
adjacent vertebral bodies, which is intended to restore disk height
between the vertebral bodies and reduce pain in the patient.

[0006] A challenge exists in the use of spinal fixation plates, however,
in that the screws employed to fix the spinal fixation plate to the
vertebral bodies have a tendency to back out from the plate over time.
One application where this is particularly worrisome is with the use of a
spinal fixation plate positioned over the anterior cervical spine. More
specifically, such backing out may cause the screws to come into unwanted
contact with the esophagus, which may lead to damage or impairment to
that organ. Another problem is that, with the screws backed out
(partially or fully), the mechanical properties of the overall construct
will become compromised, which may lead to a loss in the height of the
intervertebral space height and thereby cause pain to the patient.

[0007] Another challenge involving cervical plates in particular exists in
that it is desirable for a cervical plate to have minimal interference
with the esophagus on the anterior side of the plate while having maximum
surface area interaction with the vertebra on the posterior side of the
plate. Many cervical plates in the prior art have a uniform thickness
throughout, and to the extent that the surfaces of the plate are curved,
this curvature is intended to facilitate the interaction with the
vertebrae, often at the expense of the esophagus (in the form of
discomfort to the patient).

[0008] The present invention is directed at overcoming, or at least
reducing the effects of, one or more of the problems set forth above.

SUMMARY OF THE INVENTION

[0009] According to one broad aspect of the present invention, the present
invention accomplishes this goal by providing a surgical fixation system
including a plate, a plurality of screw members, and a corresponding
number of anti-backout elements. According to one aspect of the present
invention, the screws are prevented from backing out of the target site
after placement through the use of the anti-backout elements in
cooperation with recesses formed within the plate.

[0010] The plate includes a first surface, a second surface, and a
plurality of bone screw apertures extending between the first and second
surfaces. Each bone screw aperture has a first opening, a second opening,
and an interior channel extending therebetween. A recess is provided
within each bone screw aperture and is disposed circumferentially about
the interior channel between the first and second openings. This recess
is dimensioned to receive at least a portion of the anti-backout element.

[0011] The anti-backout element is provided as a generally circular canted
coil ring member dimensioned to be received within the recess of the
plate. The anti-backout element may be defined as having an outer
circumference, an inner circumference and an aperture bounded by the
inner circumference. Due to the canted coil nature of the anti-backout
element, each of the circumferences is independently variable. For
example, when inserted into the recess of the plate, the outer
circumference may correspond to the rigid circumference of the recess.
Upon insertion of a bone screw through the aperture, the inner
circumference may expand to accommodate passage of a head portion of the
bone screw. This expansion of the inner circumference occurs
independently from the outer circumference (unlike would occur a solid
snap ring, for example), and thus may occur without any expansion of the
outer circumference, which is prevented from expanding by the limits of
the recess. This independent expansion of the inner circumference occurs
due to the canted nature of the coils in that the individual coils
forming the anti-backout element will in effect be forced closer together
by the screw head. In other words, the force exerted by the screw head
does not cause purely radial expansion of the anti-backout element, but
rather the canted nature of the coils allow the individual coils to be
generally "flattened" against adjacent coils, in that the inner edges of
the coils (forming the inner circumference) will tend to move in one
direction, thus expanding the inner circumference, while the outer edges
of the coils (forming the outer circumference) will remain stationary,
causing no change in the outer circumference.

[0012] Each bone screw includes an anchor region, a head region, and a
neck region. The anchor region includes a generally elongated shaft with
at least one generally helical thread. Notably, the head region includes
a lip portion having a diameter that is smaller than the first opening of
the bone screw aperture, but greater than the second opening of the
aperture. Thus, the lip portion will be able to pass through the first
opening but not the second opening. The lip portion includes a generally
planar ledge portion extending generally perpendicularly from the head
region and a generally angled portion that connects the generally planar
ledge portion to the neck region. Upon insertion of the screw into the
aperture, the generally angled portion will apply a force to the
anti-backout element, allowing passage of the ledge portion therethrough.
Upon completion of insertion of the screw, the ledge portion is
completely through the anti-backout element and interacts with the
anti-backout element such that the ledge portion engages at least a
portion of the inner circumference. The generally angled portion is
prevented from passing through the second opening, and the ledge portion
is prevented from passing through the anti-backout element (absent
significant force which for example could be provided in a revision
procedure using an appropriate tool). Thus, the anti-backout element
interacts with the ledge portion to provide an anti-backout feature for
the surgical fixation system.

[0013] According to a second broad aspect of the present invention, a
surgical fixation plate is provided adapted for anterior lumbar fixation.
This plate is similar to the plate described above with the addition of a
sacral lip on the bone-engaging side of the plate. Upon implantation, the
sacral lip is dimensioned to rest on the edge of the sacrum to provide
further stability to the construct.

[0014] According to a third broad aspect of the present invention, a
surgical fixation plate is provided having a narrow configuration. Large
viewing apertures allow for improved visibility of interbody implants.
Anti-migration features on the underside of the plate allow for partial
movement of one vertebral body relative to the plate without altering the
alignment of the plate vis-a-vis that vertebral body or another vertebral
body. To accomplish this, the underside of the plate includes at least
two distinct configurations of anti-migration features surrounding bone
screw apertures. A first group involves ridges arranged in a radial
configuration, which serve to prevent any movement of the plate relative
to a first vertebral body. A second group involves ridges arranged in a
linear configuration parallel to the longitudinal axis of the plate. This
group serves to allow partial movement of the plate relative to the
adjacent vertebral body without altering the alignment of the plate (e.g.
allowing compression).

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Many advantages of the present invention will be apparent to those
skilled in the art with a reading of this specification in conjunction
with the attached drawings, wherein like reference numerals are applied
to like elements and wherein:

[0016] FIG. 1 is a perspective view of one example of a surgical fixation
system 10 according to one embodiment of the present invention;

[0017] FIG. 2 is a perspective view of a bone plate provided with
anti-backout elements forming part of the surgical fixation system of
FIG. 1;

[0018] FIG. 3 is a top plan view of the bone plate of FIG. 2;

[0019] FIG. 4 is a side view of the bone plate of FIG. 2;

[0020] FIG. 5 is a partial cross-section view of the bone plate of FIG. 3
without the anti-backout elements, taken along line 1-1 of FIG. 3;

[0021] FIG. 6 is a perspective view of an anti-backout element forming
part of the surgical fixation system of FIG. 1;

[0022] FIG. 7 is a partial cross-section view of the bone plate of FIG. 3
including the anti-backout elements, taken along line 1-1 of FIG. 3;

[0023]FIG. 8 is a perspective view of one example of a fixed-angle bone
screw forming part of the surgical fixation system of FIG. 1;

[0024] FIG. 9 is a perspective view of one example of a variable angle
bone screw forming part of the surgical fixation system of FIG. 1;

[0025] FIG. 10 is a perspective view of a second example of a variable
angle bone screw forming part of the surgical fixation system of FIG. 1;

[0026] FIG. 11 is a partial cross-section of the bone screw of FIG. 10;

[0027] FIG. 12 is a perspective view of a third example of a variable
angle bone screw forming part of the surgical fixation system of FIG. 1;

[0028] FIG. 13 is an exploded view of the variable angle bone screw of
FIG. 12;

[0030] FIG. 15 is a perspective view of a lip member forming part of the
variable angle bone screw of FIG. 12;

[0031] FIG. 16 is a top view of the surgical fixation system of FIG. 1;

[0032] FIG. 17 is a partial cross-section view of the surgical fixation
system of FIG. 16 taken along line 2-2 of FIG. 16;

[0033] FIGS. 18-19 are perspective and exploded views, respectively, of an
example of a surgical fixation system according to a second embodiment of
the present invention;

[0034] FIG. 20 is a top perspective view of an example of a surgical
fixation plate forming part of the surgical fixation system of FIG. 18;

[0035] FIGS. 21-23 are bottom perspective, side perspective, and top
views, respectively, of the surgical fixation plate of FIG. 20;

[0036] FIG. 24 is a partial cross-section view of the surgical fixation
plate of FIG. 20 (without the anti-backout element) taken along line 3-3
of FIG. 23;

[0037] FIG. 25 is a partial cross-section view of the surgical fixation
plate of FIG. 20 (with the anti-backout element) taken along line 3-3 of
FIG. 23;

[0038] FIG. 26 is a top plan view of the surgical fixation system of FIG.
20, implanted in a vertebral column;

[0039] FIG. 27 is a side view of the surgical fixation system of FIG. 26
engaged with an insertion device;

[0040]FIG. 28 is a side view of the surgical fixation system of FIG. 26
in the process of being implanted in a vertebral column;

[0041] FIG. 29 is a top perspective view of an example of a surgical
fixation plate according to a third embodiment of the present invention;

[0042] FIGS. 30-32 are bottom perspective, side, and top views,
respectively, of the surgical fixation plate of FIG. 29;

[0043] FIGS. 33-34 are top perspective and bottom perspective views,
respectively, of an example of a surgical fixation plate according to a
fourth embodiment of the present invention;

[0044] FIGS. 35-37 are perspective, side, and exploded views,
respectively, of a bone screw forming part of the surgical fixation
system of FIG. 20;

[0045] FIGS. 38-39 are perspective and side views, respectively, of a head
region of a bone screw of FIG. 35;

[0046] FIGS. 40-41 are top perspective and bottom perspective views,
respectively, of an upper ring forming part of the bone screw of FIG. 35;

[0047] FIGS. 42-43 are perspective and side views, respectively, of washer
members forming part of the bone screw of FIG. 35;

[0048] FIG. 44 is a perspective view of an example of a surgical fixation
system according to a fifth embodiment of the present invention;

[0049] FIG. 45 is a top plan view of the surgical fixation system of FIG.
44;

[0050] FIGS. 46-47 are perspective and plan views, respectively, of the
bottom side of a surgical fixation system of FIG. 44; and

[0051]FIG. 48 is a partial cross-section view of a surgical fixation
system of the present invention using a bone screw according to an
alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0052] Illustrative embodiments of the invention are described below. In
the interest of clarity, not all features of an actual implementation are
described in this specification. It will of course be appreciated that in
the development of any such actual embodiment, numerous
implementation-specific decisions must be made to achieve the developers'
specific goals, such as compliance with system-related and
business-related constraints, which will vary from one implementation to
another. Moreover, it will be appreciated that such a development effort
might be complex and time-consuming, but would nevertheless be a routine
undertaking for those of ordinary skill in the art having the benefit of
this disclosure. The surgical fixation plate disclosed herein boasts a
variety of inventive features and components that warrant patent
protection, both individually and in combination.

[0053] This invention improves upon the prior art by providing a surgical
fixation system including a surgical fixation plate, a plurality of
screws, and a plurality of anti-backout elements, wherein the
anti-backout elements are configured and dimensioned to be received
within bone screw apertures formed in the surgical fixation plate to
prevent the screws from backing out over time. As will be described
below, the anti-backout elements are capable of being easily introduced
into the bone screw apertures prior to introduction of the screws into a
given orthopedic target. Although particularly suited for use in anterior
cervical spine fixation, it will be readily appreciated by those skilled
in the art that the surgical fixation system of the present invention may
be employed in any number of suitable orthopedic fixation approaches and
procedures, including but not limited to anterior, posterior, lateral,
antero-lateral, postero-lateral, lumbar spine fixation, thoracic spine
fixation, as well as any non-spine fixation application such as bone
fracture treatment. Furthermore, although shown and described by way of
example only as used in a 4-hole, two-level plate, it will be appreciated
that such an anti-backout feature may be employed in a plate having any
number of bone screw apertures for fusion of any number of vertebral
levels.

[0054] FIG. 1 illustrates an example of a surgical fixation system 10
according to a first embodiment of the present invention. The surgical
fixation system 10 comprises a surgical fixation plate 12, a plurality of
screws 14, and a plurality of anti-backout elements 16. As will be
explained in greater detail below, the surgical fixation system 10 of the
present invention may be used to provide temporary or permanent fixation
along an orthopedic target site, including but not limited to adjacent
vertebral levels within the spine (e.g. cervical spine during anterior
fusion surgery, lumbar spine for anterior fusion surgery, etc. . . . ).
To do so, the plate 12 is first positioned over the target site such that
the screws 14 and anti-backout elements 16 may thereafter be employed to
couple the plate 12 to the target site. According to one aspect of the
present invention, the screws 14 are prevented from backing out of the
target site after placement through the use of the anti-backout elements
16 in cooperation with recesses formed within the plate 12.

[0055] Referring to FIGS. 2-5, the surgical fixation plate 12 includes a
first surface 18, a second surface 20, and a plurality of bone screw
apertures 22 extending between the first and second surfaces 18, 20. Each
bone screw aperture 22 has a first opening 24, a second opening 26, and
an interior channel 28 extending therebetween. A recess 30 is provided
within each bone screw aperture 22 and is disposed circumferentially
about interior channel 28 between the first and second openings 24, 26.
This recess is dimensioned to receive at least a portion of the
anti-backout element 16.

[0056] The plate 12 may be provided having any number of different
peripheral profiles, including but not limited to the generally
rectangular peripheral profile set forth by way of example in the figures
(and best viewed in FIG. 3). The plate 12 may also be provided with or
without viewing aperture 32 formed between the first and second surfaces
18, 20 and positioned generally in the central portion of plate 12. The
viewing aperture 32 functions to provide the ability to see or visualize
the spinal target site after the plate 12 has been secured to the
patient. It will be appreciated that the viewing aperture 34 may be
provided in any number of suitable shapes or configurations without
departing from the scope of the invention, and therefore is not limited
to the shape shown by way of example in FIG. 3.

[0057] In addition to the viewing apertures 32, the plate 12 may be
configured to include indentations 36 positioned along the lateral sides
of plate 12 in between each pair of adjacent apertures 22 as well as
indentations 38 positioned on either end of the plate 12 in between each
pair of adjacent apertures 22. The indentations 36, 38 reduce the amount
of material used in manufacturing the plate 12, and reduce the overall
profile of the plate 12 to augment the viewing capability already offered
by the viewing aperture 32. At least one insertion aperture 40 may be
provided at either end of the plate 12 for receiving at least a portion
of an insertion instrument. By way of example only, the plate 12 shown in
the attached figures includes a pair of insertion apertures 40, with one
located at each end of the plate 12. The insertion apertures 40 are
configured to engage at least a portion of an insertion device (not
shown), and thus may include any suitable feature necessary to allow such
engagement, including but not limited to threading, ridges, and recesses.

[0058] FIG. 6 illustrates one example of an anti-backout element 16
according to one embodiment of the present invention. By way of example
only, anti-backout element 16 is generally provided as a generally
circular (or annular), unbroken canted coil ring member dimensioned to be
received within the recess 30 of plate 12. The anti-backout element 16
may be defined as having an outer circumference 42, an inner
circumference 44 and an aperture 46 bounded by the inner circumference
44. Due to the canted coil nature of the anti-backout element 16, each of
the circumferences 42, 44 are independently variable. For example, when
inserted into the recess 30 of plate 12 (as shown in FIG. 7), the outer
circumference 42 may correspond to the rigid circumference of the recess
30. Upon insertion of a bone screw through aperture 46, the inner
circumference 44 may expand to accommodate passage of a head portion of
the bone screw (described in further detail below). This expansion of the
inner circumference 44 occurs independently from the outer circumference
42 (unlike would occur a solid snap ring, for example), and thus may
occur without any expansion of the outer circumference 42, which is
prevented from expanding by the limits of the recess 30. This independent
expansion of the inner circumference 44 occurs due to the canted nature
of the coils (illustrated in FIG. 6) in that the individual coils forming
the anti-backout element 16 will in effect be forced closer together by
the screw head. In other words, the force exerted by the screw head does
not cause purely radial expansion of the anti-backout element 16, but
rather the canted nature of the coils allow the individual coils to be
generally "flattened" against adjacent coils, in that the inner edges of
the coils (forming the inner circumference) will tend to move in one
direction, thus expanding the inner circumference, while the outer edges
of the coils (forming the outer circumference) will remain stationary,
causing no change in the outer circumference.

[0059] By way of example only, the anti-backout element 16 may be have any
number suitable sizes, both of the individual rings and of the outer and
inner circumferences 42, 44. The anti-backout element 16 may be formed of
any suitable biocompatible material, including but not limited to metal.
According to a preferred embodiment, in use the anti-backout elements 16
are provided within recess 30 of plate 12 prior to insertion during the
surgical procedure. It will be appreciated, however, that the
anti-backout elements 16 may alternatively be positioned within a
corresponding groove formed within the head of a screw without departing
from the scope of the present invention.

[0060]FIG. 8 illustrates an example of a fixed-angle bone screw 14
according to one embodiment of the present invention. Each screw 14
includes an anchor region 52 and a head region 54 separated by a neck
region 56. The anchor region 52 includes a generally elongated shaft 58
with at least one generally helical thread 60. The shaft 58 has a smaller
diameter than the bone screw aperture 22, the neck region 56 and thread
60 have a substantially similar diameter to that of the aperture 22, and
the head region 54 has an outer diameter greater than that of the
aperture 22. Additionally, the neck region 56 is generally cylindrical in
shape, which combined with the relative size to the aperture 22 prevents
movement of fixed-angle screw 14 once inserted into aperture 22. As the
bone screw 14 is advanced through plate 12, the thread 60 engages with
the bone securing the plate 12 to the vertebra. The head region 54 may be
equipped with any number of mechanisms for engagement with an
introduction device (e.g. a screw driver), including but not limited to
the hex-head recess 62. Moreover, although shown as a single thread 60,
it will be appreciated that the elongated shaft 58 may be equipped with
multiple threads 60 without departing from the scope of the present
invention.

[0061] Notably, the head region 54 includes a lip portion 64 having a
diameter that is smaller than the first opening 24 of the aperture 22,
but greater than the second opening 26 of the aperture 22. Thus, the lip
portion 64 will be able to pass through the first opening 24 but not the
second opening 26. Lip portion 64 includes a generally planar ledge
portion 66 extending generally perpendicularly from the head region 54
and a generally angled portion 68 that connects the generally planar
ledge portion 66 to the neck region 56. As shown in FIGS. 16-17, upon
insertion of the screw 14 into the aperture 22, the generally angled
portion 68 will apply a force to the anti-backout element 16 as described
above, allowing passage of the ledge portion 66 therethrough. Upon
completion of insertion of the screw 14, the ledge portion 66 is
completely through the anti-backout element 16 and interacts with the
anti-backout element 16 such that the ledge portion 66 engages at least a
portion of the inner circumference 44. The generally angled portion 66 is
prevented from passing through the second opening 26, and the ledge
portion 66 is prevented from passing through the anti-backout element 16
(absent significant force which for example could be provided in a
revision procedure using an appropriate tool). Thus, the anti-backout
element 16 interacts with the ledge portion 66 to provide an anti-backout
feature for the fixation system 10.

[0062] FIG. 9 illustrates one example of a polyaxial bone screw 70
according to one embodiment of the present invention. Each screw 70
includes an anchor region 72 and a head region 74 separated by a neck
region 76. The corresponding features are similar to those of the
fixed-angle screw 14 such that a repetition is not necessary. The notable
difference, however is that the neck region 76 is generally curved or
tapered to allow for movement of the screw once inserted into the
vertebra due to natural shifting of the vertebrae during normal activity
of the patient. As with the fixed-angle screw 14 described above, the
polyaxial bone screw 70 is provided with a lip portion 78 having a
generally planar ledge portion 80 extending generally perpendicularly
from the head region 74 and a generally angled portion 82 connecting the
ledge portion 80 to the neck portion 76. Thus, the polyaxial bone screw
70 is provided with the same anti-backout feature of the fixed-angle
screw 14. Similarly the head region 74 may be equipped with any number of
mechanisms for engagement with an introduction device (e.g. a screw
driver), including but not limited to the hex-head recess 75.

[0063] FIGS. 10-11 illustrate one example of a polyaxial bone screw 90
according to an alternative embodiment of the present invention. Screw 90
includes an anchor portion 92, a head portion 94, and a neck region 96
therebetween. Screw 90 differs from screw 70 in that the lip portion 98
is not an integral portion of the screw 90, and can therefore migrate
within limit about the head portion 94. Thus, when inserted into the
plate 12 at an angle, the lip portion 98 may move slightly to flushly
engage the anti-backout element 16 and create a potentially easier
insertion of the bone screw 90. Once inserted, the screw 90 has the same
anti-backout features as described above. The head region 94 may be
equipped with any number of mechanisms for engagement with an
introduction device (e.g. a screw driver), including but not limited to
the hex-head recess 95. Moreover, the head region 94 may further included
an internal threaded region 97 for engagement with a removal device in
the event of a revision or repositioning of the bone screw 90. This
feature may be present on any embodiment of bone screw described herein
without departing from the scope of the present invention.

[0064] FIGS. 12-15 illustrate another example of a polyaxial bone screw
500 according to a further alternative embodiment of the present
invention. Screw 500 includes an anchor portion 502, a head portion 504,
and a neck region 506 therebetween. Screw 500 is similar to screw 90 in
that the lip portion 508 is not an integral portion of the screw 500, and
can therefore migrate within limit about the head portion 504. Thus, when
inserted into the plate 12 at an angle, the lip portion 508 may move
slightly to flushly engage the anti-backout element 16 and create a
potentially easier insertion of the bone screw 500. Once inserted, the
screw 500 has the same anti-backout features as described above. The head
portion 504 may be equipped with any number of mechanisms for engagement
with an introduction device (e.g. a screw driver), including but not
limited to the hex-head recess 518. Moreover, the head portion 504 may
further included an internal threaded region 520 for engagement with a
removal device in the event of a revision or repositioning of the bone
screw 500.

[0065] Bone screw 500 differs from screw 90 in that the neck region 506 is
angled outward and terminates in a generally planar shelf 510 at the base
of the head portion 504. The shelf 510 serves to retain the lip portion
508 and prevent it from migrating distally along the anchor portion 502.
Lip portion 508 is generally circular in shape and includes a top surface
512, interior circumferential surface 514, and lateral circumferential
surface 516. Top surface 512 is generally flat and dimensioned to
interface with the anti-backout element 16 as described above. Interior
circumferential surface 514 is semi spherical in shape to match the
semi-spherical shape of the base of the head portion 504. Lateral
circumferential surface 516 extends in a generally curved manner from the
edge of the top surface 512 until it interfaces with the interior
circumferential surface 514. The head region further includes a

[0066] To assemble bone screw 500, the lip portion 508 is threadedly
advanced along the anchor portion 502 to the base of the neck region 506.
The circumference of the bottom end of the lip portion 508 is smaller
than the circumference of the shelf 510. However, the circumference of
the bottom end of the lip portion 508 will expand slightly as the lip
portion is advanced beyond the shelf 510, allowing a snap-fit assembly of
the bone screw 500.

[0067] FIGS. 18-19 illustrate a surgical fixation system 110 according to
a second broad aspect of the present invention. For the simplicity of
disclosure, elements of surgical fixation system 110 that are
substantially identical to elements of surgical fixations system 10 have
been assigned the same callout numbers. Surgical fixation system 110
represents an example of a specific embodiment of the present invention
adapted for anterior lumbar fixation. Surgical fixation system 110
comprises a surgical fixation plate 112, a plurality of screws 114, and a
plurality of anti-backout elements 16.

[0068] FIGS. 20-25 illustrate the plate 112 in greater detail. The
surgical fixation plate 112 includes a first surface 118, a second
surface 120, and a plurality of bone screw apertures 122 extending
between the first and second surfaces 118, 120. Each bone screw aperture
122 has a first opening 124, a second opening 126, and an interior
channel 128 extending therebetween. A recess 130 is provided within each
bone screw aperture 122 and is disposed circumferentially about interior
channel 128 between the first and second openings 124, 126. This recess
is dimensioned to receive at least a portion of the anti-backout element
16.

[0069] Plate 112 differs from plate 12 described above in that it includes
a central recessed region 132 having a plurality of apertures 134 located
on the top side of the plate, and a sacral lip member 136 provided on the
second surface 120 (i.e. vertebral contacting side) of the plate 112. The
specific features of the screws 114 are explained in greater detail
below. The anti-backout elements 16 are substantially identical to the
corresponding features of plate 12 described above and will not be
repeated here.

[0070] The recessed region 132 is generally elongated and disposed in a
generally central location within the top surface of the plate 112. The
plate 112 shown for example in FIGS. 20-23 includes a recessed region 132
having a pair of apertures 134 disposed at either end of the elongated
recessed region 132. However, it should be understood that any number of
apertures 134 may be provided if desired. Apertures 134 (and recessed
region 132) are dimensioned to engage various instrumentation 138 (FIGS.
27-28) used in the implantation of the plate 112 within the surgical
target site, including but not limited to plate inserters, drill guides,
screw inserters, etc. Moreover, the plate 112 may be provided with an
optional secondary anti-backout device (not shown) dimensioned to engage
the plate 112 at aperture 134 and extend at least partially over at least
one of the adjacent screw holes 122 in order to prevent the screw and/or
anti-backout element 16 from ejection from the screw hole. The optional
secondary anti-backout device serves primarily augment the anti-backout
capabilities of the surgical fixation system 110, and may be dimensioned
to engage at least a portion of the screw 114 and/or anti-backout element
16.

[0071] The plate 112 is further provided with a sacral lip member 136
provided on the second surface 120 (i.e. vertebral contacting side) of
the plate 112. Sacral lip member 136 is generally disposed adjacent to
the caudal-most pair of screw holes and is dimensioned to rest against
the sacrum, as shown for example in FIG. 28. This lip member allows 118
for greater stability in fixation of the plate 112 in the anterior lumbar
region.

[0072] FIGS. 29-32 illustrate an example of a surgical fixation plate 212
dimensioned for multi-level anterior lumbar fixation, for example L4-S1
fixation according to an alternative embodiment of the present invention.
The features of plate 212 are substantially similar to the features of
plate 112 described above, including a first surface 218, a second
surface 220, and a plurality of bone screw apertures 222a-c extending
between the first and second surfaces 218, 220. As with plate 112, plate
212 includes a pair of recessed regions 232 each having a plurality of
apertures 234 located on the top side of the plate, and a sacral lip
member 236 provided on the second surface 220 (i.e. vertebral contacting
side) of the plate 212. These features are substantially similar (if not
identical) to the corresponding features of plate 112, and consequently
the details will not be repeated here.

[0073] Plate 212 differs from plate 112 in that it is dimensioned for
multi-level anterior lumbar fixation, for example L4-S1 fixation. Thus
the plate includes at least three fixation regions 240, 242, 244. For
example, first fixation region 240 is disposed at one end of the plate
and is dimensioned to be placed over a first vertebral body (e.g. S1
vertebra). First fixation region 240 includes a first pair of bone screw
apertures 222a similar to bone screw apertures 22 described above. First
fixation region 240 further includes the sacral lip member 236 on the
second surface 220.

[0074] The second fixation region 242 is positioned in the interior of
plate 212 and is dimensioned to be placed over a second vertebral body
(e.g. L5 vertebra). Second fixation region 242 includes a pair of bone
screw apertures 222b similar to bone screw apertures 22 described above.
The second fixation region 242 is separated from first fixation region
240 by a first body portion 246 of plate 212.

[0075] The third fixation region 244 is positioned at the opposite end of
the plate 212 from the first fixation region 240 and is dimensioned to be
placed over a third vertebral body (e.g. L4 vertebra). The third fixation
region 244 includes a pair of bone screw apertures 222c similar to bone
screw apertures 22 described above. The third fixation region is
separated from the second fixation region by a second body portion 248 of
plate 212. Second body portion 248 is greater in size that first body
portion 246 to account for the anatomical structure of the spine in that
particular region (L4-S1). However, specific dimensions of the plate 212,
including relative sizes and lengths of first and second body portions
246, 248 may differ depending on specific spinal levels of implantation.
Furthermore, plate 212 may be provided without sacral lip member 236
without departing from the scope of the present invention. Although
described in regards to a specific example of placement within the spine
(e.g. L4-S1 fixation), plate 212 may be used in other regions of the
spine and elsewhere throughout the body

[0076] FIGS. 33-34 illustrate an example of a plate 312 dimensioned for
anterior lumbar fixation according to an alternative embodiment of the
present invention. The features of plate 312 are substantially similar to
the features of plate 112 described above, including a first surface 318,
a second surface 320, and a plurality of bone screw apertures 322
extending between the first and second surfaces 318, 320. As with plate
112, plate 312 includes a central recessed region 332 having a plurality
of apertures 334 located on the top side of the plate. These features are
substantially similar (if not identical) to the corresponding features of
plate 112, and consequently the details will not be repeated here. Plate
312 differs from plate 112 in that it does not include a sacral lip
member on the second surface 320 (i.e. vertebral contacting side) of the
plate 312. By way of example only, plate 312 may be used in fixation
surgeries involving the lumbar region of the spine and not including the
sacrum. Plate 312 may also be used in other regions of the spine and
elsewhere within the body without departing from the scope of the present
invention.

[0077] FIGS. 35-37 illustrate an example of a bone screw 114 according to
one embodiment of the present invention for use with the various bone
plate embodiments described above. Bone screw 114 includes a head 150,
neck region 152, elongated shaft 154, cap 156, and washer 158. The shaft
154 includes threads 160 for threaded purchase into a bony segment (e.g.
vertebral body).

[0078] Referring to FIGS. 38-39, the head 150 includes a first ledge 162,
a circumferential recess 164, a second ledge 166, and a tool engaging
recess 168 disposed on the top of the head 150. The circumferential
recess 164 is provided between the first and second ledges 162, 166 and
is dimensioned to receive the washer 158. The distance between the first
and second ledges 162, 166 (i.e. the height dimension of the recess 164)
is greater than the height dimension of the washer 158 to allow for a
controlled movement of the washer within the recess 164. The tool
engaging recess 168 may be shaped in any shape necessary to correspond to
a screwdriver (not shown). The neck region 152 extends below the first
ledge 162 and may vary in size and width depending upon the specific type
of screw required (e.g. fixed angle or variable angle). A fixed angle
screw will have a neck region 152 with a greater width than a variable
angle screw, to ensure the fixed angle screw does not move relative to
the bone screw aperture of the plate.

[0079] FIGS. 40-41 illustrate an example of the cap 156 in greater detail.
Cap 156 is generally circular and includes an interior shelf 170
dimensioned to interact with the second ledge 166 of the head 150. The
cap 156 functions to increase the width of the top of the head 150 within
the bone screw aperture and also to help retain the washer 158 within the
circumferential recess 164.

[0080] FIGS. 42-43 illustrate an example of the washer 158 in greater
detail. Washer 158 is generally circular in shape and includes a top
surface 172, bottom surface 174, interior circumferential surface 176,
and lateral circumferential surface 178. Top and bottom surfaces 172, 174
are generally flat and are dimensioned to interface with the second and
first ledges 162, 166, respectively. The top surface 172 is further
dimensioned to interface with the anti-backout element 16 as described
above. The top and bottom surfaces 172, 174 each have maximum
circumferences defined by the circumferences of the outer edges of each.
In the embodiment shown, the maximum circumference of the top surface 172
is greater than the maximum circumference of the bottom surface 174. The
interior circumferential surface 176 is dimensioned to interact with the
interior of the circumferential recess 164 of the head 150. The lateral
circumferential surface 178 extends between the top and bottom surfaces
172, 174 in a generally angled manner.

[0081] The washer 158 of the current embodiment functions similarly to the
lip member 64 described above in relation the bone screw 14. Thus, the
washer 158 will be able to pass through the first opening 124 but not the
second opening 126 of the plate 112. Upon insertion of the screw 114 into
the aperture 122, the lateral circumferential surface 178 will apply a
force to the anti-backout element 16 as described above, allowing passage
of the top surface 172 therethrough. Upon completion of insertion of the
screw 114, the top surface 172 is completely through the anti-backout
element 16 and interacts with the anti-backout element 16 such that the
top surface 172 engages at least a portion of the recess 130. The
generally lateral circumferential surface 178 is prevented from passing
through the second opening 126, and the top surface 172 is prevented from
passing through the anti-backout element 16 (absent significant force
which for example could be provided in a revision procedure using an
appropriate tool). Thus, the anti-backout element 16 interacts with the
top surface 172 to provide an anti-backout feature for the surgical
fixation system 110.

[0082] FIGS. 44-47 illustrate an example of a surgical fixation system 410
according to a third embodiment of the present invention. For the
simplicity of disclosure, elements of surgical fixation system 410 that
are substantially identical to elements of surgical fixations system 10
have been assigned the same callout numbers. Surgical fixation system 410
comprises a surgical fixation plate 412, a plurality of screws (not
pictured), and a plurality of anti-backout elements 16. Plate 412 differs
from plate 12 described above in that it has narrower size dimensions,
allowing for only one fixation screw per vertebral level, and includes
several additional features described below. Although not pictured, the
screws are substantially the same as the screws 14 described above. The
specific features of the screws 14 and anti-backout elements 16, as well
as their interaction with the plate 412 are substantially identical to
the corresponding features of plate 12 and will not be repeated here.

[0083] As will be explained in greater detail below, the surgical fixation
system 410 of the present invention may be used to provide temporary or
permanent fixation along an orthopedic target site, including but not
limited to adjacent vertebral levels within the spine (e.g. cervical
spine during anterior fusion surgery, lumbar spine for anterior fusion
surgery, etc. . . . ). To do so, the plate 412 is first positioned over
the target site such that the screws 14 and anti-backout elements 16 may
thereafter be employed to couple the plate 412 to the target site.
According to one aspect of the present invention, the screws 14 are
prevented from backing out of the target site after placement through the
use of the anti-backout elements 16 in cooperation with recesses formed
within the plate 412.

[0084] Referring to FIGS. 44-47, the surgical fixation plate 412 includes
a first surface 418, a second surface 420, and a plurality of bone screw
apertures 422 extending between the first and second surfaces 418, 420.
The bone screw apertures 422 exhibit the same features as the bone screw
apertures 22 as described above. Placement of the plate 412 in situ is
such that each bone screw aperture 422 aligns with a distinct vertebral
body. As such, the plate 412 shown in FIGS. 44-47 is configured for a
"two-level" fixation in that the plate 412 spans two intervertebral
spaces with one vertebral body between. However, plate 412 may be
configured such that it applies to a single level fixation (i.e. one
intervertebral space between adjacent vertebrae) or multiple levels
without departing from the scope of the present invention.

[0085] The plate 412 may be provided having any number of different
peripheral profiles, including but not limited to the generally
rectangular peripheral profile having a longitudinal axis A1 set
forth by way of example in the figures (and best viewed in FIG. 45). The
plate 412 has a length dimension ranging between 20 mm and 50 mm, a width
dimension ranging between 10 mm and 12 mm, and a thickness dimension
ranging between 1 mm and 2.5 mm. The plate 412 includes a viewing
apertures 432 formed between the first and second surfaces 418, 420 and
between adjacent bone screw apertures 422. The viewing apertures 432
function to provide the ability to see or visualize the spinal target
site after the plate 412 has been secured to the patient. It will be
appreciated that the viewing aperture 432 may be provided in any number
of suitable shapes or configurations without departing from the scope of
the invention, and therefore is not limited to the shape shown by way of
example in FIG. 45.

[0086] In addition to the viewing apertures 432, the plate 412 may be
configured to include indentations 436 positioned along the lateral sides
of plate 412 in between each pair of adjacent apertures 422. The
indentations 436 reduce the amount of material used in manufacturing the
plate 412, and reduce the overall profile of the plate 412 to augment the
viewing capability already offered by the viewing aperture 432. Either or
both ends of the plate 412 may include a sloped surface 438 resulting in
a leading edge 440 having a thickness of approximately 1 mm. This 1 mm
leading/trailing edge further reduces the profile of the plate 412 at the
margins and minimizes interference with nearby anatomical structures.

[0087] Referring to FIG. 46, the second surface 420 is configured to
engage the vertebral bodies. As such, the second surface 420 contains
textured regions 450, 452, 454 surrounding the bone screw apertures 422.
Each textured region 450, 452, 454 include a plurality of anti-migration
features configured to limit or prevent movement of the plate relative to
the adjacent vertebral bodies. The first textured region 450 is located
around a first bone screw aperture 422 positioned toward one end of the
plate 412, and includes a plurality of anti-migration features 456
arranged radially around the aperture 422. Anti-migration features 456 as
shown by way of example only are elongated ridges (of varying lengths)
having a generally triangular cross-section. However, other shapes are
possible. The shape and configuration of anti-migration features 456
allow for rigid placement of the plate 412 against a vertebral body, and
prevent movement of the plate relative to the vertebral body such that
the desired alignment is maintained.

[0088] The second textured region 452 is located around a second bone
screw aperture 422, for example the middle bone screw aperture 422 in the
example shown in FIGS. 46-47. The second textured region 452 includes a
plurality of anti-migration features 458 arranged linearly and parallel
to the longitudinal axis A1 of the plate 412 (FIG. 45).
Anti-migration features 458 as shown by way of example only are elongated
ridges (of varying lengths) having a generally triangular cross-section.
However, other shapes are possible. The shape and configuration of
anti-migration features 458 allow for limited movement of the plate 412
relative to the adjacent vertebra in a direction parallel to longitudinal
axis A1 of the plate 412, but prevents movement of the plate in any
other direction. This feature is important because it allows for
compression of the adjacent vertebrae without affecting the alignment of
the plate 412.

[0089] The third textured region 454 is located around a third bone screw
aperture 422, for example the aperture 422 located at the other end of
the plate 412. In this example, the third textured region 454 includes
anti-migration features 460 having an identical shape and arrangement to
anti-migration features 458 of textured region 452. Although shown by
example as having one textured region 450 having a radial configuration
and two textured regions 452, 454 having linear configurations to allow
for compression, any combination of radial and linear configurations are
possible depending on the particular needs of a patient. Generally,
however, plate 412 will have at least one textured region having a radial
configuration and at least one textured region having a linear
configuration.

[0090] In all the embodiments described herein, the anti-backout element
functions to resist backout tendencies in bone screws. The anti-backout
element does not, however, lock a bone screw to a plate. This is because
the bone screw is removable from the bone screw aperture through
application of a sufficient amount of force to pull the lip member (or
washer) through the anti-backout member. Due to the nature of the canted
coil ring and dimensions of the lip member (or washer) described above,
the force required to remove an inserted bone screw is greater than the
force required to insert the bone screw. Nevertheless, the bone screw may
be inserted and/or removed in a single-step process--no separate
manipulation of the anti-backout element is required.

[0091] While the invention is susceptible to various modifications and
alternative forms, specific embodiments thereof have been shown by way of
example in the drawings and are herein described in detail. For example,
FIG. 48 shows one example of a bone screw 14 according to a still further
alternative embodiment of the present invention, in which screw 14
includes a proximal lip member 100. It should be understood, however,
that the description herein of specific embodiments is not intended to
limit the invention to the particular forms disclosed, but on the
contrary, the invention is to cover all modifications, equivalents, and
alternative falling within the spirit and scope of the invention as
described herein.